Re: [PATCH v2 bpf 03/11] bpftool: use a local bpf_perf_event_value to fix accessing its fields

From: Alexander Lobakin <aleksander.lobakin@intel.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
	Song Liu <songliubraving@fb.com>,
	Kumar Kartikeya Dwivedi <memxor@gmail.com>, <bpf@vger.kernel.org>,
	<netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<tpgxyz@gmail.com>
Subject: Re: [PATCH v2 bpf 03/11] bpftool: use a local bpf_perf_event_value to fix accessing its fields
Date: Wed, 7 Jun 2023 18:18:20 +0200	[thread overview]
Message-ID: <a45e22d7-9178-ebb5-ef4b-691606dd7560@intel.com> (raw)
In-Reply-To: <ZH+e9IYk+DIZzUFL@google.com>

From: Nick Desaulniers <ndesaulniers@google.com>
Date: Tue, 6 Jun 2023 14:02:44 -0700

> On Thu, Apr 21, 2022 at 12:39:04AM +0000, Alexander Lobakin wrote:
>> Fix the following error when building bpftool:
>>
>>   CLANG   profiler.bpf.o
>>   CLANG   pid_iter.bpf.o
>> skeleton/profiler.bpf.c:18:21: error: invalid application of 'sizeof' to an incomplete type 'struct bpf_perf_event_value'
>>         __uint(value_size, sizeof(struct bpf_perf_event_value));
>>                            ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:13:39: note: expanded from macro '__uint'
>> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helper_defs.h:7:8: note: forward declaration of 'struct bpf_perf_event_value'
>> struct bpf_perf_event_value;
>>        ^
>>
>> struct bpf_perf_event_value is being used in the kernel only when
>> CONFIG_BPF_EVENTS is enabled, so it misses a BTF entry then.
>> Define struct bpf_perf_event_value___local with the
>> `preserve_access_index` attribute inside the pid_iter BPF prog to
>> allow compiling on any configs. It is a full mirror of a UAPI
>> structure, so is compatible both with and w/o CO-RE.
>> bpf_perf_event_read_value() requires a pointer of the original type,
>> so a cast is needed.
>>
> 
> Hi Alexander,
> What's the status of this series? I wasn't able to find a v3 on lore.

Hi,

Sorry, I haven't been working on my private/home kernel projects for
quite a long. As Quentin mentioned, he took some patches from the series
into his own set. I'd support that one rather than mine.

> 
> We received a report that OpenMandriva is carrying around this patch.
> https://github.com/ClangBuiltLinux/linux/issues/1805.
> 
> + Tomasz
> 
> Tomasz, do you have more info which particular configs can reproduce
> this issue? Is this patch still necessary?
> 
>> Fixes: 47c09d6a9f67 ("bpftool: Introduce "prog profile" command")
>> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
>> Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Thanks,
Olek